Chicago's springs starting earlier and getting warmer

The Chicago area got lucky on St. Patrick's Day.

The high at O'Hare Airport soared to 73 degrees, a full 25 degrees above average. It was also the warmest day in five months. The last time we were that warm was the middle of October last year.

Our first 70 degree highs of the year are coming earlier on average. The mean date of the first 70 degree high over the past 50 years is April 1. We beat it Thursday by almost two weeks.

Springs in Chicago are getting warmer. Climate Central analyzed the change in spring temperatures for 242 towns and cities in the United States and found that 97% saw an increase since 1970. Nearly half of the locations studied saw an impressive jump of 2 degrees or more.


Chicago's increase was more modest but still impressive. Our springs have warmed 1.2 degrees from 1970 to 2021.

All of our seasons have warmed during this period. This means our seasons are shifting. Spring is arriving earlier and pinching off winter. Climate Central says this shift can cause: 

  • Longer pest and allergy seasons: An early spring, and an early last freeze can lengthen our growing season. That means that related nuisances like mosquitoes and pollen can appear earlier in the year, and stick around for longer.
  • Mismatch timing in nature: Spring warming can also disrupt the timing of ecologically-important events. For example, some migratory bird species are not keeping pace with the earlier arrival of spring—potentially impacting their food availability and breeding success. The consequences of mismatch timing are an active area of study.

Eight of the first 17 days of meteorological spring have been above average so far. We can expect (on average) more above normal days as the season warms. Just under 70% of the locations in the study have seen an increase of at least seven more days above their 1991-2020 spring normal temperature since 1970. Chicago has seen an increase of five more days above normal from 1970 to 2021.

The vast majority of our country has seen their springs get warmer over the past fifty years. The only exceptions are portions of North and South Dakota. The biggest jump in temperatures have occurred in Reno, Nevada (6.8 degrees), Las Vegas (6.2 degrees), and El Paso, Texas (5.9 degrees).